U.S. patent application number 14/403598 was filed with the patent office on 2015-05-28 for electrophoresis gel cassette with at least one removable section.
This patent application is currently assigned to GE HEALTHCARE BIO-SCIENCES AB. The applicant listed for this patent is GE HEALTHCARE BIO-SCIENCES AB. Invention is credited to Erik J Bjerneld, Lennart Bjorkesten, HENRIK Bjorkman, Sofia Edlund, Camilla Larsson, Peter Oliviusson, Henrik Ostlin, Ola Ronn, Owe Salven, Stefan Sjolander, Kajsa Stridsberg-Friden.
Application Number | 20150144492 14/403598 |
Document ID | / |
Family ID | 49673708 |
Filed Date | 2015-05-28 |
United States Patent
Application |
20150144492 |
Kind Code |
A1 |
Bjorkesten; Lennart ; et
al. |
May 28, 2015 |
ELECTROPHORESIS GEL CASSETTE WITH AT LEAST ONE REMOVABLE
SECTION
Abstract
Electrophoresis gel cassette comprising a first and a second
face wall member and one or more side wall members, defining a gel
compartment for a gel member with a first and second face, wherein
the first face wall member has high gel adhesion compared to the
second face wall member, whereby a gel member molded in the
cassette will stay attached to the high gel adhesion face wall
member when the cassette is opened, and wherein the first face wall
member is provided with at least one removable section to expose a
section of the first face of the gel member, the removable section
of the first face wall member having lower gel adhesion compared to
the non-removable part of the first face wall member.
Inventors: |
Bjorkesten; Lennart;
(Uppsala, SE) ; Salven; Owe; (Uppsala, SE)
; Larsson; Camilla; (Uppsala, SE) ; Bjerneld; Erik
J; (Uppsala, SE) ; Edlund; Sofia; (Uppsala,
SE) ; Ostlin; Henrik; (Uppsala, SE) ;
Sjolander; Stefan; (Uppsala, SE) ; Stridsberg-Friden;
Kajsa; (Uppsala, SE) ; Ronn; Ola; (Uppsala,
SE) ; Oliviusson; Peter; (Uppsala, SE) ;
Bjorkman; HENRIK; (Uppsala, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GE HEALTHCARE BIO-SCIENCES AB |
UPPSALA |
|
SE |
|
|
Assignee: |
GE HEALTHCARE BIO-SCIENCES
AB
UPPSALA
SE
|
Family ID: |
49673708 |
Appl. No.: |
14/403598 |
Filed: |
May 31, 2013 |
PCT Filed: |
May 31, 2013 |
PCT NO: |
PCT/SE2013/050631 |
371 Date: |
November 25, 2014 |
Current U.S.
Class: |
204/616 |
Current CPC
Class: |
B01L 9/527 20130101;
G01N 27/44743 20130101; G01N 27/44756 20130101; G01N 27/44704
20130101 |
Class at
Publication: |
204/616 |
International
Class: |
G01N 27/447 20060101
G01N027/447 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2012 |
SE |
1250557-4 |
Claims
1. Electrophoresis gel cassette comprising a first and a second
face wall member and one or more side wall members, defining a gel
compartment for a gel member with a first and second face, wherein
the first face wall member has high gel adhesion compared to the
second face wall member, whereby a gel member molded in the
cassette will stay attached to the high gel adhesion face wall
member when the cassette is opened, and wherein the first face wall
member is provided with at least one removable section to expose a
section of the first face of the gel member, the removable section
of the first face wall member having lower gel adhesion compared to
the non-removable part of the first face wall member.
2. Electrophoresis gel cassette according to claim 1 wherein the
side wall members are formed integrally with one of the face wall
members forming a cassette body.
3. Electrophoresis gel cassette according to claim 1 wherein one
removable section is arranged to expose a section of the first face
of the gel member essentially corresponding to the separation
zone.
4. Electrophoresis gel cassette according to claim 1, wherein one
or more removable sections are arranged to expose a buffer contact
section of the first face of the gel member.
5. Electrophoresis gel cassette according to claim 1 comprising
integrated buffer compartments and optionally electrodes.
6. Electrophoresis gel cassette according to claim 1, wherein at
least one of the first and a second face wall members is formed of
a plastic film
7. Electrophoresis gel cassette according to claim 6 wherein the
first face wall member is formed of two or more laminated layers of
plastic film, wherein the first layer facing the gel compartment
has one or more openings formed therein which are covered by one or
more pealable sections of the second layer.
8. Electrophoresis gel cassette according to claim 7 wherein the
first layer is comprised of a rigid polymer film with adhesive
layers applied to both faces and the second layer is comprised of a
rigid polymer film.
9. Electrophoresis gel cassette according to claim 8 wherein the
first layer is comprised of a PET film with adhesive EVA layers
applied to both faces and the second layer is comprised of a PET
film.
10. Electrophoresis gel cassette according to claim 7, wherein the
side wall members are formed integrally with the second face wall
member forming a cassette body with a rim around the side wall onto
which the first face wall member is removeably attached.
11. Electrophoresis gel cassette according to claim 6, wherein at
least one of the first and second layer is provided with peal tabs
to facilitate removal of the same.
12. Electrophoresis gel cassette according to claim 1, wherein the
first face wall member is provided with high gel adhesion around
the perimeter of the gel to facilitate removal from the
cassette.
13. Electrophoresis gel cassette according to claim 1 comprising a
precast gel.
14. Electrophoresis gel cassette according to claim 1, wherein at
least one of the first and a second face wall member is comprised
of an optically transparent material to allow imaging of the gel
without opening the cassette.
15. Electrophoresis gel cassette according to claim 1, wherein the
first face wall member is formed as a rigid support arranged to
preserve the shape of and to facilitate handling of the gel member
after it has been removed from the cassette.
16. Electrophoresis gel cassette according to claim 1, wherein the
first face wall member is provided with an alignment structure
defining a positional reference for alignment of the gel cassette
and the gel member after it has been removed from the cassette.
17. Electrophoresis gel cassette according to claim 1, wherein the
first face wall member is provided with an identification code.
Description
TECHNICAL FIELD
[0001] This invention is generally related to thin film deposition
methods. More particularly, the invention is related to thin film
deposition methods that include depositing material on a surface
and etching away portions of that material in an effort to control
the film of material left on the surface.
BACKGROUND
[0002] Thin film deposition methods are commonly used for the
fabrication of semiconductor and other electrical, magnetic, and
optical devices. However, the quality (material properties) of thin
films deposited by conventional methods are often not comparable to
bulk material, particularly in cases of low temperature deposition,
such as when temperatures at the substrate must be kept much lower
than the melting point of the films to avoid thermal damage to the
devices. This is often a result of imperfections in the
as-deposited film structure and morphology.
[0003] Various on Assisted Deposition (IAD) methods have been
developed to improve the quality of deposited thin film properties
at low substrate temperatures. The deposition source may be an
evaporation source (thermal or electron-beam), magnetron
sputtering, and the ion assist provided by an ion source, such as,
for example, a Kaufman-type gridded ion source or a gridless ion
source, such as an End Hall source.
[0004] IAD processes are useful for improving properties of films
deposited on flat substrates because energetic ions stimulate and
cause atomic displacement at the surface, as well as surface atom
diffusion and desorption at low substrate temperatures. Control of
the incidence angle of the ions and flux of the ions relative to
that of the depositing neutral particles may be useful to affect
film structure (in particular to increase the film density and/or
modify film stress). The ion energies used for ion bombardment in
the conventional IAD process are typically at or near the
sputtering threshold of the material on the surface and the ion
flux is relatively low compared to the deposition flux.
[0005] Another known ion assisted method is Dual Ion Beam
Deposition, in which a primary deposition ion beam source sputters
material from a deposition target to the substrate and a secondary
"assist" ion beam source is directed to the surface of the
substrate. This method, like other ion assist methods, has the
advantage that the angle of incidence of the assist ion beam can be
controlled to affect the film properties. Yet another type of IAD
method used for plasma-based thin film deposition processes such as
sputtering is biased substrate deposition. In this method, ions in
the plasma are directed to the substrate by an electric field.
However, in this method the ion bombardment of the substrate occurs
at essentially normal incidence. In experiments undertaken by the
present inventors, Aluminum Oxide films formed by this method tend
to form seams at the edges of the step features, where material
deposited on the step feature at a first relative angle meets
material deposited in surrounding areas at a different relative
angle. The resulting seam defect is seen in the micrograph of FIG.
1A. The low quality of material adjacent to these seams is
particularly evident when wet etching is used to remove poor
quality deposited material, which preferentially etches the
material found along the seams leaving voids as are visible in FIG.
1B.
[0006] These examples represent a typical situation, as deposition
of thin films commonly is performed on three dimensional surfaces.
Three dimensional surfaces are often involved at some stage of
fabrication for most devices, for example, as a result of an
accumulation of multiple steps of patterned deposition and etching.
Variation in deposited thickness over substrate features can result
in problems due to poor conformal coverage, build-up of surface
irregularities, trapped voids, seams, and similar problems in the
corners of the features. A conformal film is one that has a
thickness that is the same everywhere. Variations in device
dimensions and properties become more critical as device dimensions
are scaled down in size.
[0007] It is generally appreciated that the deposited film
properties such as density, stress, and optical indexes are
dependent on deposition incidence angle. Poor film properties seem
to be associated with higher incidence angles. The quality and
conformality of films deposited on 3-D surfaces may thus be
improved to some extent by controlling the angle of deposition on
the substrate (tilting the substrate relative to direction of
flux). In a tilted deposition process the substrate is typically
also rotated in order to obtain uniform deposition around the 3-D
features across the substrate surface. This technique is used in
thin film evaporation and ion beam deposition systems, and has more
recently has been extended to sputtering systems with the
popularization of low pressure sputtering technology. Desirable
properties of the film deposited on the bottom and sidewall
features of a 3-D feature have been observed for incidence angles
of up to, but not exceeding, a critical angle of 55-65 degrees for
either bottom and sidewall surfaces. However, control of incidence
angles can be achieved only at very beginning stage of the growth.
During growth, the shape of the sidewall evolves, and eventually
results in glancing deposition angle on the bottom as well as on
sidewall surfaces. As a result, quality of deposited material in
the corner may deteriorate.
[0008] In one known example, thin films are deposited using
magnetron sputtering, with the sputtering source at a 45 degree
angle to the substrate, and with the substrate rotating to
accomplish even coating across the surface. This approach does
improve the quality of sidewall coverage on three dimensional
features because the sidewalls are deposited with material at an
incidence angle nearer to normal. However, experiments conducted by
the present inventors have revealed that even an angled deposition
process of this kind eventually forms seam lines between field and
feature deposition due to the evolution of the sidewall shape
described above, albeit less pronounced than those formed in the
process described with reference to FIGS. 1A and 1B. These seam
lines can be seen in FIG. 2A. Subsequent evaluation by wet etching
that is preferential to the lower quality material leaves voids
along these seam lines at the periphery of the underlying three
dimensional features as seen in FIG. 2B.
[0009] Another known ion etch assisted deposition method uses a
dual ion beam approach, in which a beam with ion energies well
above the material's sputtering threshold is directed to the
surface during material deposition. This approach can be used to
improve conformality of films deposited on 3-D surfaces.
Specifically, in Improved step coverage by ion beam resputtering,
J. Vac. Sci. Technol. 18(2), Harper, J. M. E., G. R. Proto, and P.
D Hoh (March 1981) (the "Harper paper"), SiO2 films were deposited
by an IAD method on a Nb substrate having approximately 90 degree
steps, using a dual ion beam deposition system (IBD) in which the
angle of incidence of the depositing neutral particles was 20
degrees from the substrate normal and the angle of incidence of the
ions from the "assist" (etch) source was 20 degrees from the
substrate normal or 40 degrees from the direction of the depositing
angle. The general configuration of the system is seen in FIG. 3A.
According to the Harper paper, the step coverage was improved,
however, the methods in the Harper paper failed to achieve a
satisfactorily conformal film. Films deposited according to these
prior art methods show a re-entrant overhang of the coating 9 at
features in the substrate 8, as seen in FIG. 3B, and/or tend to
form a thin facet on the corner of the step, as seen in FIGS. 3C
and 3D. Thus, there remains a need to improve upon this and the
other known methods for ion etch assisted deposition.
[0010] Known methods have thus failed to provide films of desired
quality, including films on surfaces with 3-D topology.
Particularly, known methods generally result in films having
incomplete conformality and uniformity of coverage over the
substrate. Thus, a need exists in the art for improvements relating
to thin film deposition methods.
SUMMARY
[0011] The forgoing limitations of the prior art can be overcome
according to the present invention by depositing the film using a
combination of a beam of energetic particles that forms a film on
the surface, and a beam of ions that simultaneously etches the
surface of the patterned wafer mounted on a rotated or sweeping
substrate. The present invention comprises a method of utilizing
differences in the deposition and etch rates at different angles to
achieve improved film deposited film properties. Specifically, the
system configuration is adjusted to provide (a) approximately equal
incidence angles of deposition and etch beam fluxes at any position
on the feature; and (b) deposition (etch) angles of incidence
obtained on the main surfaces of the features (e.g. base and
sidewall of step or trench features) that are substantially equal.
The deposition and etch fluxes are adjusted in a way that etch rate
prevails over deposition rate at critical, and higher, incidence
angles, thus removal of poor quality material is achieved.
[0012] According to an embodiment of the invention, an ion etch
assisted deposition apparatus is used to deposit a thin film upon a
substrate having a three dimensional feature. The apparatus
includes an ion etching source and deposition source arranged at
similar angles relative to the substrate and at an angle .alpha.
relative to each other, where the angle .alpha. is selected to be
substantially equal the supplement of the angle .alpha.' formed
between the three dimensional feature on the substrate and the
substrate surface.
[0013] Two modes of substrate motion may be used to accomplish
uniform coating of three dimensional features: (a) rotation, and
(b) sweeping. Sweeping motion can be suitable for three dimensional
features which are elongated along one axis
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIGS. 1A and 1B illustrate films deposited with a prior art
process at a normal angle to the surface, before and after wet
etching;
[0015] FIGS. 2A and 2B illustrate films deposited with a prior art
process at an angle of approximately 45 degrees to the surface,
before and after wet etching;
[0016] FIG. 3A is an illustration of a dual ion beam etch assisted
deposition apparatus in accordance with the prior art, and FIGS.
3B, 3C and 3D illustrate step coverage achieved with this
apparatus;
[0017] FIG. 4 is a schematic representation of a dual beam system
for depositing a thin film in accordance with principles of the
present invention, showing the preferred angle .alpha. between the
dual ion sources;
[0018] FIG. 5 is a diagram of deposition rate and etch rate of
Aluminum Oxide by a magnetron sputtering deposition source and an
End Hail ion beam etching source, respectively, shown as a function
of the relative tilt angle between the source and substrate
normal;
[0019] FIGS. 6A, 6B and 6C illustrate three relative angular
configurations of the deposition and ion etch sources of FIG. 4, in
which the sources are arranged at angles .alpha. which are selected
to be supplementary to the angle .alpha.' between three dimensional
features and the substrate as respectively shown in FIGS. 6D, 6E
and 6F;
[0020] FIG. 7 is a schematic representation of an alternative
system for depositing a thin film that may permit greater ion etch
uniformity or power in some embodiments;
[0021] FIG. 8 is a plan view of a system for depositing a thin film
showing greater detail on the structures involved;
[0022] FIG. 9 shows steps for depositing a thin film on a surface
of a substrate according to the invention disclosed herein;
[0023] FIGS. 10A, 10B show the step coverage obtained on a
substrate with features with sidewall angles .alpha.' of
approximately 90 degrees, in the center and near the edge of the
substrate showing the absence of seam lines before wet etching, and
FIGS. 10C and 10D show the same structures after wet etching, for
showing the absence of voids; and
[0024] FIGS. 11A and 11B show thick Chromium deposition on a
substrate having vertical sidewalls at a similar angle of
.alpha.'=90 degrees, showing the absence of seam lines and
effective fill and planarization;
[0025] FIGS. 12A and 12B show the step coverage obtained on a
substrate with isolated features with sidewall angles .alpha.' of
approximately 90 degrees, in the center and near the edge of the
substrate, showing the absence of seam lines, and FIGS. 12C and 12D
show similar good step coverage on trenches in the center and near
the edge of the substrate;
[0026] FIG. 13 is a schematic illustration of a sweeping motion in
accordance with principles of the present invention, illustrating
the movement relative to the orientation of the elongated axis of
the substrate features during sequential sweeping, rotation (index
change) and sweeping steps; and
[0027] FIG. 14 shows deposition on a substrate having an elongated
feature which extends on an axis perpendicular to the plane of the
photograph, showing the absence of seam lines and effective fill
and even coverage.
DETAILED DESCRIPTION
[0028] Referring to the figures, and beginning with FIG. 4, a
system for depositing a thin film in accordance with principles of
the present invention is shown and is generally indicated by the
numeral 10. The system 10 may be situated in an enclosed chamber,
as is known in the thin film deposition art.
[0029] The system 10 includes a deposition source 12, which is the
source of material that is to be deposited as a thin film on a
surface. Any suitable deposition source may be used, and any
suitable material may be used therewith. For example, a sputter
target may serve as the source. The deposition source 12 directs
particles of material along an axis 14 toward the surface of a
substrate 16 that receives the material. Separately, an ion source
18 creates a beam of ions for etching the material deposited on the
surface of the substrate 16, the beam of ions being directed along
an axis 20 toward the surface of the substrate 16. The axis 14 and
the axis 20 may represent the centerline of the deposition and etch
beams, respectively. They generally intersect at the substrate 16
and may occupy the same plane. The relative position of the
deposition source 12 and the ion source 18 is adjustable, with the
adjustment of such being explained more fully below. The ion source
may be an End Hall source or gridded ion source. It may also be
substituted by any directed source of energetic particles capable
of etching the substrate, e.g. a plasma beam etch or a neutral beam
source.
[0030] The substrate 16 may be any substrate for receiving a thin
film applied thereto, and may include 3-D topographic features,
including, for example, steps or trenches. The substrate 16 is
supported by a suitable structure for receiving material from the
deposition source 12 and ions from the ion source 18. The substrate
16 may be tilted (as shown at 24) to an angle with respect to the
deposition source 12 and the ion source 18. In particularly, the
substrate tilt direction 24 may be along an axis that is orthogonal
to both axes 14 and 20 of the deposition and etch beams,
respectively: e.g., assuming axes 14 and 20 are in the same plane,
the substrate surface normal 24 lies in the same plane. The
substrate 16 may also be rotated around a central rotation axis 22
that is generally perpendicular to the surface of the substrate 16.
It is assumed that the substrate surface is planar and the tilt
angular orientation of the substrate defines the tilt angular
orientation of the "flat" surfaces of the 3-D features, e.g. the
bottoms or tops of steps or trenches.
[0031] Referring now to FIG. 5, the deposition rate of source 12,
and etch rate of source 18, and the angle of tilt of the deposition
or etching axis away from perpendicular to the surface of a
substrate can be discussed. While the data in this figure is
specific to Aluminum Oxide deposited by magnetron sputtering and
etched by an End Hall ion beam source, the trends shown are
representative of many other materials and deposition and etch
sources as well. It will be appreciated that the flux of particles
created by the deposition source 12 represents a measure of the
flow of material from the deposition source, and relates to the
deposition rate at which material is added to the substrate 16. The
flux of the ion beam created by the ion source 18 represents a
measure of the flow of ions from the ion source, and relates to the
etch rate at which material is removed from the substrate 16. Any
suitable flux of the energetic particle beam and the ion beam may
be used as long as the relative ratio of these fluxes is determined
according to the methods of this invention, as described below.
[0032] It will be appreciated from FIG. 5 that the rates of
deposition and etch are a strong function of the angle of incidence
of the deposition and etch sources to the substrate. As can be
seen, the deposition rate is at its greatest when the axis 14 of
the deposition source is perpendicular to the substrate surface,
which corresponds to a tilt angle of 0 degrees in the graph of FIG.
5. The deposition rate falls monotonically as the tilt angle
increases, to a value of zero when the tilt angle reaches 90
degrees. The etch rate evidences an opposite trend, increasing
monotonically with the tilt angle until the tilt angle reaches
approximately 45 degrees, then decreasing monotonically.
[0033] As can be seen in FIG. 5, when, for example, the deposition
and etch beams are incident on the substrate at the same angle, the
etch and deposition fluxes may be selected such that there is a
first range of tilt angles in which the deposition rate is greater
than the etch rate, and a second range of tilt angles in which the
etch rate exceeds the deposition rate. When thus adjusted, the
apparatus precludes the deposition of material at angles within the
second range, because any material deposited at this tilt angle is
essentially immediately removed by the simultaneous etch process.
Thus, adjustment of the deposition and etch rates to have the two
ranges seen in FIG. 5 enables the deposition to be constrained to
occur only in a desired range of tilt angles, such as tilt angles
less than the critical angle above which poor quality of the
deposited film is obtained, e.g. 65 degrees, as shown in FIG. 5 for
alumina deposition.
[0034] In applying this concept to deposition on 3-D features, we
require the deposition configuration to be arranged such that the
main surfaces of the features (e.g. the "flat" surfaces and
sidewalls of step or trenches) are subject to net quality
deposition, i.e. to the first range of angles (less than the
critical angle) described above. At the same time, other surfaces
formed as a result of growth of deposited material at high
incidence angles to the deposition beam resulting in poor quality
deposition are exposed to the second range of angles mentioned
above, i.e. these surfaces are etched instead of deposited. This is
achieved for example by adjusting the angles of the deposition and
etch beams on the substrate surface and on the sidewalls of the
features to be equal; such a symmetrical treatment condition is
also important to achieve a conformal coating (same net deposition
thickness on sidewall and flat surfaces).
[0035] In practice, the thickness and properties of the deposited
film will be determined by the cumulative effect of a number of
factors, some of which are not considered in detail here, in
particular resputtering of material from the bottom and sidewall
and changes in the features as a result of growth. Thus in some
useful or even preferred configurations the angular conditions may
vary somewhat from those described above.
[0036] It is noteworthy that the etch source and deposition source
will generally occupy different physical positions such that, at
any instant in time, when etching three dimensional features some
portions of said features will be exposed to different azimuthal
angles of etch and deposition. However, if the polar deposition and
etch incidence angles incident on the substrate surface are equal
and the substrate is rotated by a sufficient number of revolutions
during the coating process, the average etch and deposition angles
at any point are essentially the same, which is sufficient.
[0037] In practical implementations, illustrated diagrammatically
in FIGS. 6A-F, the system 10 of FIG. 4 permits deposition of high
quality coatings upon surfaces having a variety of 3-D features. To
ensure operation of the sources so that the simultaneous deposition
and etch creates a high quality film and prevents growth of low
quality film, the tilt angles of the sources 12 and 18 may be
selected to correspond to the relative angles of the surfaces to be
coated on the 3D features of the substrate. For example, as shown
in FIG. 6A-2, the substrate features may include a base 22a which
intersects with a sidewall 24a at a right angle, i.e., an angle
.alpha.' of ninety degrees. Such a configuration is possible for
both an isolated feature that generally extends upward from the
rest of the surface, as well as a trench feature that extends
downward below the rest of the surface. For this case, as seen in
FIG. 6A the sources are placed at an angle of a of ninety degrees
relative to each other. Secondly, the substrate is tilted such that
the deposition and etch beams both bisect the angle between the
base and the sidewall, resulting in equal deposition and etch
angles at these main surfaces. In this case, both deposition and
etching upon the main surfaces will operate in the range of 45
degrees to the substrate normal or at 45 degrees to the surface of
the substrate. Thirdly, the deposition and etch fluxes are adjusted
as shown in FIG. 5, in which the deposition rate is equal to the
etch rate at a critical angle (65 degrees in the figure) above
which the deposited film quality is poor. Thus the deposition rate
exceeds the etch rate on the main surfaces (at 45 degree incidence
angle to the substrate normal) whereas the etch rate exceeds the
deposition rate at angles above said critical angle.
[0038] As shown in FIG. 6B, a base 22b may intersect with a
sidewall 24b at an angle .alpha.' that is somewhat less than ninety
degrees (e.g. 80 degrees). Such a configuration is possible for
either step or trench features. For this case, to achieve equal
angles of deposition and etch on the base and sidewalls of the
features, as seen in FIG. 6B, the sources are placed at an angle
.alpha. (e.g. 100 degrees) relative to each other, where a is
supplementary to .alpha.', i.e., .alpha.+.alpha.'=180 degrees, and
secondly the substrate is tilted to an angle of .alpha.'/2 (e.g. 40
degrees) from the deposition and etch beams to the substrate
surface. As in the case above, the deposition and etch beams bisect
the angle between the base and the sidewall. The angle of incidence
of the deposition and etch beams to these surfaces, relative to the
substrate normal (as referred to in FIG. 5), is .alpha./2 (e.g. 50
degrees). The deposition and etch fluxes are adjusted as described
for FIG. 6A.
[0039] And as shown in FIG. 6C, a base 22c may intersect with a
sidewall 24c at an angle .alpha.' that is somewhat greater than
ninety degrees (e.g. 100 degrees). Such a configuration is possible
for both a step or trench feature. In such a case, as before, to
achieve equal angles of deposition and etch on the main surfaces,
the sources are located at an angle .alpha.(e.g. 80 degrees)
relative to each other, where .alpha.+.alpha.'=180 degrees, as seen
in FIG. 6F and the tilt angle of the substrate is adjusted such
that the angle of each beam bisects the angle between the base and
the sidewall, i.e. the angle to the substrate surface is .alpha.'/2
(e.g. 50 degrees) The angle of incidence to the substrate normal of
the deposition and etch beams on the main features (as referred to
in FIG. 5) is .alpha./2 (e.g. 40 degrees), well within the range of
high quality deposition. The deposition and etch rate fluxes are
adjusted as described for FIG. 6A,
[0040] Generally, the relative position of the deposition source 12
and the ion source 18 is adjusted so that the angular separation
between the deposition source axis 14 and the ion source axis 20 is
generally supplementary to the angle .alpha.' of one or more
features on the surface of the substrate 16. Thus, where the base
22a and sidewall 24a intersect at a right angle (FIG. 6A-2), the
angle between the deposition source axis 14 and the ion source axis
20 is generally also a right angle (FIG. 6A).
[0041] Similarly, where the base 22b and sidewall 24b intersect at
an angle .alpha.' that is less than ninety degrees (FIG. 6E), the
angle between the deposition source axis 14 and the ion source axis
20 is generally greater than ninety degrees, for example,
180-.alpha.' (FIG. 6B).
[0042] And where the base 22c and sidewall 24c intersect at an
angle .alpha.' that is greater than ninety degrees (FIG. 6F), the
angle between the deposition source axis 14 and the ion source axis
20 is generally less than ninety degrees, for example, 180-.alpha.'
(FIG. 6C).
[0043] Generally, the substrate 16 may be tilted with respect to
the deposition source 12 and the ion source 18 so that the
deposition source axis 14 and the ion source axis 20 are an equal
angular distance from the substrate rotation axis 22. Thus, as
shown in FIGS. 4 and 6A-6C, the deposition source axis 14 is spaced
from the substrate rotation axis 22 (which is collinear with the
substrate surface normal 26 passing through the substrate center
point) by half of .alpha., or .alpha./2, and the ion source axis 20
is similarly spaced from the substrate rotation axis 22/surface
normal 26 by half of .alpha., or .alpha./2, where
.alpha.=180-.alpha.'.
[0044] Turning to FIG. 7, another embodiment of a system for
deposition a thin film is shown and is indicated by the numeral
10a. The system 10a includes the features of system 10 discussed
above, as well as a second ion source 19 that creates a beam of
ions that are directed along an axis 21 toward the surface of the
substrate 16. The second beam may improve uniformity across the
substrate surface, and/or assist in the generation of sufficient
energetic ions to accomplish a desired etch rate.
[0045] Turning to FIG. 8, a more detailed embodiment of a system
for deposition of a thin film is shown and is indicated by the
numeral 30. The system 30 includes magnetron 32 as a deposition
source and a multi-beamlet large gridded ion source 34 as an ion
source. A substrate 36 for receiving a thin film is positioned on a
fixture 38, which provides for tilting and rotation of the
substrate 36. Fixture 38 is also capable of performing a sweep
motion around a defined azimuthal index angle, sweeping in a
specified range of azimuthal angles relative to the index angle,
and both positive and negative directions, as is illustrated and
discussed below with reference to FIG. 13. A collimator 40 is
provided between the magnetron 32 and the fixture 38.
[0046] Referring now to FIG. 9, a method for depositing a thin film
on a surface of a substrate according to the invention disclosed
herein is performed using a system that includes a deposition
source, an ion source, and a substrate, the substrate being
supported and capable of tilting with respect to the deposition
source and the ion source, and being capable of rotating about a
central rotation axis. If not already known, the 3-D topographic
features of the surface of the substrate that will receive the thin
film are investigated so as to determine an angle of intersection
.alpha.' for a feature of critical interest on the surface of the
substrate. The deposition source is positioned so that a beam of
energetic particles of material created thereby is directed at the
substrate along a deposition source axis, and the ion source is
positioned so that a beam of ions created thereby is directed at
the substrate along an ion source axis. The angular separation
between the deposition source axis and the ion source axis is
adjusted in proportion to the angle .alpha.'. In some embodiments,
the angular separation between the deposition source axis and the
ion source axis is adjusted so as to be substantially supplementary
to .alpha.'. The substrate may be tilted so that the deposition
source axis and the ion source axis are equally angularly spaced
from the central rotation axis about which the substrate may be
rotated, and thus generally at an angle of .alpha.'/2 from the
plane of the substrate. The flux of material from the deposition
source and the flux of material from the ion source may be adjusted
so as to provide an etch rate equal to or higher than a deposition
rate when the incidence angles are approximately equal to or
greater than a critical incidence deposition angle, which critical
angle is the angle beyond which the final film properties begin
deteriorating at an unsatisfactory rate.
[0047] Exemplary thin films were prepared according to the
teachings contained herein, as will be detailed below. The
description of following examples provides illustrations only and
does not limit the scope of the present invention.
Example 1
[0048] Al203 films were deposited on 8'' Si wafer with plurality of
1 .mu.m height isolated SiO2 features with shape close to
rectangular.
[0049] The deposition was performed in a chamber that was
configured with pulsed DC magnetron and End Hall ion beam source.
An Aluminum target and an Argon/Oxygen gas mixture was used for
sputtering. The samples were deposited using the "metal mode" of
deposition, operating with high speed O2 partial pressure feedback
control. The use of high speed partial pressure control eliminates
the transition to a "poisoned" target typically seen without active
feedback and allows for Al2O3 deposition rates up to 5.times.
higher than those obtained with the same target power in poisoned
mode. Argon was used as feed gas for End Hall source. The system
used a tiltable substrate fixture to allow for variable process
angle deposition (with respect to substrate surface normal). The
substrate temperature was maintained by the Flowcool.TM. helium
backside gas cooling system. The system has a fixture shutter to
allow for in-situ pre-clean of the target prior to deposition.
[0050] Configuration was set up: angle .alpha. between axis of
sputtered material and axis of ion beam was set I to 90.degree.,
and corresponded to a 90.degree. angle .alpha.' between bottom and
side wall in the corners of the feature; incidence angles for
deposition and etch were each 45.degree. or .alpha.'/2. The fluxes
of the sputtered beam, and the beam of ions were adjusted to
provide etch rate equal to deposition rate at a 65 degree critical
incidence deposition angle: Magnetron sputtering power was 6.5 kW;
End Hall beam voltage and current were 200V and 15 A
respectively.
[0051] The results of this process include: Optical spectra: index
n.about.1.66, extinction coefficient k.about.0, which evidence good
film quality; net deposition rate: 600 A/min; uniformity over 8''
area: 2.5%. A SEM image of the rectangular feature cross-section is
shown in FIGS. 10A-10D. The image of the as-deposited film (FIG.
10A, 108) demonstrated no seam lines or crevices, uniform contrast
is evidence of uniform structure (no pores, good density) around
the corner area, good conformality in the center and at the edge
(8'' diameter). The image of the samples after standard etch test
(FIG. 10C, 10D) demonstrated good quality with no voids.
Example 2
[0052] Cr films were deposited on an 8'' Silicon wafer with
plurality of 1 .mu.m high isolated Silicon dioxide (SiO2) features
and trenches with shape close to rectangular, trench aspect ratio
(AR).about.1:2.
[0053] The deposition was performed in a chamber that was
configured with pulsed DC magnetron, and End Hall source (see
Example 1). A Chromium target and an Argon gas were used for
sputtering. Argon was used as a feed gas for the End Hall
source.
[0054] Configuration was set up: angle .alpha. between axis of
sputtered material and axis of ion beam was set to 90.degree., and
corresponded to the angle .alpha.' of 90.degree. between bottom and
side wall in the corners of the feature; incidence angles for
deposition and etch were .alpha.'/2=45.degree., The fluxes of the
sputtered beam, and the beam of ions were adjusted to provide etch
rate equal to deposition rate at a 65 degree critical incidence
deposition angle: Magnetron sputtering power was 2.5 kW; End Hall
beam voltage and current were 175V and 12 A, respectively.
[0055] Results of Example 2 are seen in FIGS. 11A-11B in a "fill"
or planarization application: Thickness of the deposited film
.about.2.3 .mu.m, resistivity .about.20 ohm/cm2 is evidence of good
quality; deposition rate: 300 A/min; uniformity over 8'' area: 3%.
A SEM image of a feature with rectangular cross-section is shown in
FIG. 11A--the image demonstrated no seam line, or crevices, uniform
no pores, good density around the corner area, and good
conformality. A SEM image of a film/trench (AR=1:2) structure (FIG.
11B) also showed good density and conformality, no crevices,
excellent planarization effect.
[0056] Further results of Example 2 for a "seed layer" application
are seen in FIGS. 12A-12D. Thickness of the deposited film
.about.0.3 .mu.m, uniformity over 8'' area --3%; SEM images of the
rectangular feature (FIGS. 12A and 12B), and trench cross-section
(FIGS. 12C and 12D) demonstrated conformal deposition; corners are
filled by material. Good results are seen in the substrate center
(FIGS. 12A and 12C) as well as at edges (FIGS. 12B and 12D).
Example 3
[0057] Cr films were deposited on an 8'' diameter Silicon wafer
with plurality of 1 .mu.m high isolated Silicon dioxide (SiO2)
features with long axis and shape close to rectangular.
[0058] The deposition was performed in a chamber that was
configured with pulsed DC magnetron, and End Hall source (see
Example 2). A Chromium target and an argon gas were used for
sputtering. Argon was used as a feed gas for the End Hall
source.
[0059] The chamber was set up with the angle .alpha. between the
axis of sputtered material and axis of ion beam equal to
90.degree., corresponding to the angle .alpha.' of 90.degree.
between bottom and side wall in the corners of the feature;
incidence angles for deposition and etch were
.alpha.'/2=45.degree.. The fluxes of the sputtered beam, and the
beam of ions were adjusted to provide etch rate equal to deposition
rate at a 65 degree critical incidence deposition angle: Magnetron
sputtering power was 5 kW; End Hall beam voltage and current = were
130V and 12 A, respectively.
[0060] The substrate included elongated 3D features which are
symmetrical to a long axis direction as illustrated
diagrammatically in FIG. 13. For elongated features in such a
configuration, equal deposition shape/thickness is accomplished on
each elongated side of the feature using sweeping mode, as
illustrated in FIG. 13, which uses a sweeping motion 42 and
indexing motion 44 in combination. A typical range of sweeping
motion 42 is .+-.30-70.degree., and ranges up to 90 degrees; an
approximately .+-.45.degree. sweep range 42 is illustrated in FIG.
13. Sweeping is performed around two or more azimuthal index
angles, which are alternately selected by indexing motion 44 which
rotates the wafer to each azimuthal index angle. At each azimuthal
index angle sweeping motion is repeated a number of times. In the
case illustrated in FIG. 13 there are two azimuthal index angles
and the wafer is indexed between these angles with a 180.degree.
index motion 44. Any number of sweep cycles can be programmed, and
more than two azimuthal index angles may be defined for a
particular substrate feature configuration. The azimuthal index
angles are set to obtain the desired orientation of the critical
dimension of the feature to the deposition and etch beams for
uniform coating of said feature. In the case of elongated features,
the critical feature dimension is typically the long axis of the
feature. The initial substrate azimuthal index angle is set such
that the long axis/axes of the substrate features are orthogonal to
the direction of the deposition and etch beams (axes 14 and 20 in
FIG. 4) and parallel to the tilt axis of the substrate fixture. At
this azimuthal index angle, one elongated side of the feature is
exposed to deposition and shadowed from etch and the opposite
elongated side of the feature is exposed to etch and shadowed from
deposition. After 180 degree reorientation, the side previously
exposed to deposition and shadowed from etch will be exposed to
etch and shadowed from deposition, and vice versa. During
processing, sweep motion 42 is performed around this azimuthal
index angle within an azimuthal angle sweep range of, e.g.,
45.degree., for a number of cycles. Then the substrate is rotated
44 to a new azimuthal index angle--in the illustrated case rotating
180.degree. to a second index angle, and sweeping motion 42 is
repeated at the new index angle for a number of cycles. The
sweeping motion 42 and index motion 44 cycle occurs multiple times
to deposit desired thickness of conformal identical coatings on
both A and B sides.
[0061] For Example 3, the initial azimuthal index angle for
sweeping was set perpendicular to the elongated axis of the
substrate features as seen in FIG. 13. Sweeping was performed in a
range of .+-.45.degree., and 60 sweep cycles were performed at each
of two 180.degree. opposed azimuthal index angles.
[0062] Results of Example 3 show the applicability of the invention
for forming conformal films over step features without voids.
Thickness of the deposited film .about.1 .mu.m, resistivity
.about.17 ohm/cm2 (evidencing good quality); deposition rate --:
650 A/min; uniformity over 8'' area: --4%. A SEM image of a feature
with rectangular cross-section is shown in FIG. 14--the image
demonstrated no seam line, or crevices, uniform no pores, good
density around the corner area, and good conformality.
[0063] Electrical resistivity of the Chrome films deposited
according the present invention averages approximately 20-25
ohm/cm.sup.2, lower than the approximately 35-40 ohm/cm.sup.2
average resistivity of the film deposited by magnetron sputtering
with no etch assist, and matching good quality Cr bulk resistivity.
With higher ion etch power, the resistivity of films decreases to
below 20 ohm/cm.sup.2 due to densification of the film.
[0064] To demonstrate the beneficial effects of etch assist, a Cr
film was deposited, without etch assist, on a substrate with
isolated features having sidewalls at a 90 degree angle from the
substrate plane. A fixture tilt of approximately 45 degrees was
utilized to match the conditions used according with the invention.
The deposited film evidenced a purely columnar structure, with
crevices at the feature corners (similar to those seen in FIGS. 2A
and 2B). The resistivity of the film was approximately 35
ohm/cm.sup.2 compared with the resistivity of 20 ohm/cm.sup.2 or
below achieved with the present inventive process.
[0065] It will be appreciated that a novel and inventive surface
processing system, and novel applications therefor, have been
described here. Applicant does not intend by this description and
the details thereof to limit the scope of the invention being
sought to be protected, but rather, that protection is to be
defined by reference to the following claims.
* * * * *